PRIOR ART
It is well known to digitize an analog signal by PCM (pulse coded modulation) at the transmission end and to reproduce the original analog signal by receiving the digitized PCM signal at the receiving end.
As shown in FIG. 7, at the transmission end, there are provided a sampling circuit 1 by sampling the analog signal to be transmitted in response to sampling pulses to provide a PAM pulse in proportion to the amplitude of the input signal waveform, a quantization circuit 2 to quantize the amplitude of the PAM pulse into 2.sup.7 (=128) to 2.sup.8 (=256) steps in accordance with a predetermined rule, and an each step coding circuit (PCM pulse coding) 3 for converting each step into combinations of presence or absence of unit pulses comprising 7 bits or 8 bits binary code.
Now, shown in FIG. 8 is the PCM pulse coding steps. However, the PCM pulse as shown in FIG. 8 is represented by 2.sup.4 (=16) steps as an example.
Amplitude value of the stepped PCM pulse is now represented by decimal "105". This is equal in binary to 1.times.2.sup.6 +1.times.2.sup.5 +0.times.2.sup.4 +1.times.2.sup.3 +0.times.2.sup.2 +0.times.2.sup.1 +1.times.2.sup.0, or "1101001". This means that the amplitude is represented by presence ("1") or absence ("0") of 7 unit pulses. Such PCM coded pulse signal is transmitted to the receiving end through a transmission path 4.
On the other hand, reverse operations to the transmission end are performed at the receiving end. Firstly, the pulse signal coded into PCM pulse is decoded by a decoding circuit 5 to obtain a PAM pulse which is reproduced to the analog signal through a filter circuit 6 for removing quantization noise.